Smart cards are well known devices that include a card body into which is embedded an integrated circuit (IC). The integrated circuit is designed to store data that can be used, inter alia, to provide the card with electronic identification, authentication, data storage and application processing capabilities. As a result, smart cards, which are also commonly referred to as integrated circuit cards or chip cards, are widely used in commerce to provide information and/or application processing capabilities in connection with, but not limited to, bank cards, credit cards, health insurance cards, driver's licenses, transportation cards, loyalty cards and membership cards.
Smart cards of the type as described above transmit data stored on the integrated circuit using either (i) a direct contact interface (the resultant products being commonly referred to in the art as contact smart cards), (ii) a contact-free interface (the resultant products being commonly referred to in the art as contactless smart cards) or (ii) a hybrid of the two aforementioned interfaces (the resultant products being commonly referred to in the art as dual-interface smart cards).
Contactless and dual-interface smart cards typically utilize an antenna embedded in the card body as a non-contact means for transmitting communication signals between the integrated circuit and an associated card reader. The antenna is commonly constructed as a conductive wire that is arranged in a coiled, or spiraled, configuration within the card body. Each free end of the wire is often arranged into a dense configuration, such as a tightly wrapped coil, spiral, W-shape, or zig-zag formation, to form a suitable contact terminal.
To achieve functionality of the smart card, the integrated circuit needs to be coupled to the antenna. Traditionally, the integrated circuit is connected to the antenna through either direct connection or inductive coupling.
To facilitate its handling and connection, an integrated circuit designed for use in a smart card is traditionally mounted on a lead frame to form a unitary IC module. As part of its construction, an IC module typically includes contact pads on the underside of the lead frame, with each contact pad serving as a suitable connection surface.
Accordingly, direct connection relies upon connecting a conductive element (e.g. a wire, conductive epoxy or combination thereof) between the contact pads on the IC module and the contact terminals for the antenna. However, in order to directly connect the contact pads on the IC module to the contact terminals of the antenna, a cavity is typically milled in the card body to a depth that is sufficient to at least partially expose the antenna contact terminals.
With the contact terminals for the antenna exposed, direct connection is commonly made between the antenna and the IC module using a variety of different connection techniques.
As an example, in U.S. Pat. No. 8,640,965 to C. M. Sutera, the disclosure of which is incorporated herein by reference, there is shown a dual-interface smart card that electrically connects an IC module to exposed sections of an antenna using a pair of opposing, stapled-shaped, conductive elements, with one conductive element being permanently welded to a contact pad on the IC module and the other conductive element being permanently welded to the antenna. Each conductive element includes a pair of resilient spring arms that maintain electrical connection between the contact pad and the antenna even upon movement of the IC module relative to the card body. To provide further redundancy of connection between each contact pad and the antenna, the resilient spring arms of the opposing conductive elements are encapsulated with a supply of conductive filler material.
As another example, in U.S. Pat. No. 6,881,605 to C. K. Lee, the disclosure of which is incorporated herein by reference, there is disclosed a method of forming a dual-interface smart card that establishes connection between an IC and an antenna coil by pulling out the two free ends of the antenna coil from the core sheet, and securing each of the extracted free ends of the antenna to the integrated circuit, for example, by soldering or thermocompression bonding.
As referenced briefly above, direct connection of the IC module to the antenna first requires that a cavity be milled into one surface of the card body to expose the antenna contact terminals. As a critical aspect of the milling process, the cavity must be precisely milled to the proper depth. If the cavity is not milled to the requisite depth, the antenna contact terminals would not be adequately exposed for direct connection. By contrast, if the cavity is milled beyond the requisite depth, the antenna contact terminals may become damaged and therefore compromise the overall operability of the smart card.
However, it has been found that milling a cavity into the card body to the proper depth is often rendered challenging due to natural variances in card thickness resulting from, inter alia, material thickness tolerances of individual layers in the card body as well as process tolerances during lamination of the card body. As a result of these variances in card thickness, the antenna contact terminals of a smart card are not always located at the same depth relative to a card surface.
Accordingly, methods for determining proper antenna depth in a card body are required. Currently, various techniques exist for milling the cavity to the proper depth to allow for subsequent connection of the antenna to the IC module.
In one well-known technique, milling is performed in an incremental fashion, with the milling tool being withdrawn from the card after each step (i.e. increase in depth) to visually inspect whether the antenna contact terminals have been adequately exposed.
In another well-known technique, a pair of pilot holes, each of limited cross-sectional diameter, is simultaneously milled into the card body in alignment with the antenna contact terminals. Once both of the milling bits used to create the pilot holes contact the antenna, there is a measurable change in conductivity between the milling bits, which indicates proper milling depth. With the depth of the milling tool locked relative to the card (i.e. in the Z direction), formation of the cavity in the desired geometry is achieved by replacing each milling bit and/or moving the milling tool relative to the card body within the locked plane.
In another well-known technique, which is shown in U.S. Pat. No. 6,174,113 to R. Brechignac et al., the disclosure of which is incorporated herein by reference, an electric potential is generated in the antenna. Once the milling tool contacts the antenna, there is a measurable change in the electric potential of the milling tool, which indicates proper milling depth. With the depth of the milling tool locked relative to the card (i.e. in the Z direction), formation of the entire cavity in the desired geometry can be achieved.
Although well known in the art, the aforementioned milling techniques have been found to suffer from certain shortcomings. In particular, the incremental milling technique has been found to be both time-consuming and labor-intensive in nature, the pilot-type milling technique has been found to suffer from a lack of precision due to machine tolerances (since the contact surfaces of the milling bits need to be acutely adjusted to lie in the same plane) and the electric potential-type milling technique has been found to suffer from a lack of precision due to interference from unanticipated electromagnetic fields present in the immediate environment.